The present invention relates generally to a color filter making use of a hologram and, more particularly, to a hologram color filter designed to improve the efficiency of utilization of backlight, etc., by using a hologram as well as a liquid crystal display device with a built-in hologram color filter and a fabrication process of such a hologram color filter.
So far, backlight for displaying purposes has been indispensable for a color liquid crystal display device with a built-in color filter. When the color liquid crystal display device is immediately illuminated by white light from behind, however, the efficiency of utilization of the white light is very low for the following major reasons:
1. The area occupied by black matrixes except the cell of each color is large, and thus light striking on them will be wasted. PA1 2. Of the white light incident onto each pixel, the color components passing through the color filters R (red), G (green) and B (blue) is limited to one color. Thus, other complementary color components will again be wasted. PA1 3. Each color filter has light loss due to absorption.
To solve such problems, it has been known in the art to locate a microlens array 2 in front of a color filter 1, as shown in FIG. 17 as an example, to converge white backlight 3 onto color filter cells R, G and B, thereby improving the efficiency of utilization of the backlight 3. In connection with FIG. 17, it is understood that reference numeral 4 represents black matrixes located between the color filters R and G, and G and B.
Even with this technique, however, the problem 2 mentioned above remains unsolved, because it is impossible to separate the white light 3 into its spectral components for the illumination of the color filter cells R, G and B. Moreover, the problem 3 mentioned above remains unsolved, because reliance is still on the color filter 1.
There is another plausible process in which a hologram is located in front of each pixel such that the red, green and blue components are selectively converged onto the red, green and blue color filters, respectively. According to this process, it is possible to improve the efficiency of utilization of backlight because each pixel is illuminated by the white light while it is separated into its spectral components.
For this holographic process, however, it is required that one hologram be subjected to trichromatic multiple exposure, or that three holograms, each for one color, be superposed together at the same position. The disadvantages of this process are that the trichromatic multiple exposure gives rise to a lowering of the efficiency of diffraction of the hologram for each color, and the superposition of three holograms incurs difficulty in alignment, and is very troublesome to do as well.